Various processes for production of L-aspartic acid from fumaric acid and ammonia (to create diammonium fumarate) using microorganisms having aspartase activity have been published. For example see--Chibata, I; Tosa, T.; Sato, T. Comprehensive Biotechnology Vol. 3 Ed. Murray Moo-Young, Permagon, 1985. In these published processes, the L-aspartic acid is usually recovered by precipitation of L-aspartic acid crystals resulting from the addition of a mineral acid such as sulfuric acid to the reaction solution, and separation of the crystals. However in these published processes, a large amount of waste salt(s), such as ammonium sulfate, is generated as a by-product of the precipitation. The production of these salts is undesirable from an environmental perspective and causes the undesirable loss of ammonia.
U.S. Pat. No. 4,560,653 ('653) issued Dec. 24, 1985, discloses a process for the production of L-aspartic acid wherein aspartase or an aspartase-producing microorganism acts upon fumaric acid and ammonia. L-aspartic acid is precipitated by addition of maleic acid and filtered from the solution and the mother liquors are recycled. This '653 patent discloses the use of a chemical catalyst for maleic acid to fumaric acid isomerization.
As an alternative catalyst for maleate to fumarate isomerization, enzyme-containing organisms with maleate isomerase activity can be used. For examples see--Otsuka, K. Agr. BioL. Chem., 25(9), 1961, 726.--Scher, W. and Jakoby, W. B. J. Biol. Chem., 244(7), 1969, 1878. This catalyst reportedly gives high conversions of maleic acid salts to fumaric acid salts at basic pH.
U.S. Pat. No. 3,391,059 which issued Jul. 12, 1968, discloses an enzyme containing organism with maleate isomerase activity and aspartase activity to produce L-aspartic acid directly from maleic acid.
The art of preparing L-aspartic acid economically and efficiently with minimal or no environmental adverse impact continues to be of interest to industry.